1 ABSTRACT 2 Cardiovascular diseases (CVD) are the leading cause of death in women in the US. Women differ from men in 3 rates and timing of CVD and show a stronger association between CVD and metabolic syndrome. This 4 difference suggests that gender-specific factors may moderate the underlying pathophysiology of CVD. We 5 propose that lactation could be one such women-specific factor. Multiple observational studies have linked 6 breastfeeding with reduced maternal cardiometabolic disease later in life; however, the underlying mechanisms 7 for the beneficial effect of lactation remain unknown. Our central hypothesis is that high levels of oxytocin 8 produced during lactation protect breastfeeding mothers against cardiovascular diseases later in life. 9 We were the first to report significantly lower systolic and diastolic blood pressure; less adipose tissue; better 10 cardiac ejection fraction, output, and diastolic function; and lower concentrations of circulating cardiovascular 11 risk markers in mice that lactated compared to mice that did not lactate. Oxytocin (OXT) is a neuropeptide that 12 triggers uterine contractions, the milk let-down reflex during lactation, and plays a central role in maternal 13 behavior and social affiliation. OXT in physiological situations, such as pregnancy and lactation, induces its 14 own synthesis and release. In our model, we found significantly increased circulating OXT levels and mRNA 15 expression in mice that lactated. The objective of this study is to further define the mechanisms affecting 16 maternal cardiovascular and metabolic outcomes after lactation-induced OXT production. We will test 3 17 hypotheses: 1) OXT-stimulating events during lactation ? suckling and maternal-pup interaction ? are required 18 for dams to develop maternal cardioprotective phenotype later in life; 2) that higher levels of OXT in 19 postpartum lactated mice is a result from activation of central OXT-OXTR system; 3) administration of 20 exogenous OXT to nonlactating mice in the immediate post-delivery period will rescue the cardioprotective 21 phenotype with or without pre-existing chronic disease. Aim 1 is designed to mimic the bottle-feeding situation 22 in non-breastfeeding women; we will use mice with their nipples surgically removed. In Aim 2 we will use 23 conditional knockout mice (flox-Cre recombinase system) that are Oxtr deficient in the brain. In Aim 3 the 24 hypothesis will be tested in obesity-hypertension model. Longitudinal in vivo experimental procedures will 25 include measuring fasting glucose and blood pressure, and assessing cardiac function with echocardiogram 26 and adipose tissue using micro-computed micrography. In vitro, we will utilize organ explant and vascular 27 reactivity studies. In summary, our proposal will define the mechanisms by which lactation affects maternal 28 health later in life and quantify the causal effect of breastfeeding on maternal cardiovascular and metabolic 29 health. The results of our study may lead to further mechanistic explorations of the role of lactation in maternal 30 health, which could be directly translated into interventions to prevent CVD in women.